U. S. Pat. No. 4,917,978, issued on Apr. 17, 1990, to Ritt et al., describes a method of manufacturing a screen assembly for a CRT by the electrophotographic screening (EPS) process. The method described in the aforementioned patent includes a "fusing" step followed by a "fixing" step to increase the adherence of the phosphor screen elements to an underlying organic photoconductive (OPC) layer deposited on the interior surface of the CRT faceplate panel. In the fusing step, vapors of a solvent are permitted to contact and soak the OPC layer and the polymeric coupling agent that coats the phosphor materials, to render the layer and the coating tacky. Vapor soaking takes on the order of 4 to 24 hours. The panels are then dried and "fixed" by spraying multiple layers of polyvinyl alcohol (PVA) in an alcohol-water mixture onto the fused phosphor elements. Each spray application requires about 2 to 5 minutes to achieve complete screen coverage. The "fixed" screens are then filmed, either by convention spray or emulsion filming. It has been determined that the PVA spray applications tend to move the phosphor elements slightly, which might be unacceptable, depending on the amount of movement.
U.S. Pat. No. 5,474,866, issued to Ritt et al., on Dec. 12, 1995 describes a method for fixing the phosphor elements to the underlying OPC layer, by electrostatically spraying a suitable fixative. The fixative dissolves the OPC layer in such a manner that the phosphor elements are at least partially encapsulated by the OPC layer, without causing any movement of the phosphors. An inspection of the phosphor side of the faceplate panel, with a UV source, after fixing, stimulates the phosphor elements to emit visible light. The visible light output from the phosphor screen elements shows patterns consisting of light and dark regions, with several gradations of shading therebetween. The dark regions indicate greater encapsulation, or coverage, of the phosphor elements by the OPC layer during fixing. In regions where the OPC layer encapsulates the phosphor elements, it absorbs some of the incident UV radiation and also absorbs some of the emitted visible light, thereby reducing the light output of the encapsulated phosphor elements, making them appear darker than the phosphor elements that are only partially encapsulated. After fixing, the phosphor screen is filmed by providing a layer of a suitable acrylic resin that overlies the phosphor elements and forms a smooth surface on which an aluminum layer subsequently is deposited. Inspection of filmed phosphor screens with a UV source also stimulates the phosphor elements to emit visible light. Because the filming material completely covers the phosphor elements, the light output of the phosphor elements, after filming, is more attenuated than before filming. This difference in light output provides an indication of the thickness and uniformity of the filming layer. It is desirable to utilize the light output information, provided by UV exposure of both the fixed and filmed phosphor screens, to establish process controls and optimize the fixing and filming steps in the manufacturing operation.